It is conventional practice to provide reverse buckling discs comprising an annular peripheral flange portion bounding an integral concave/convex dome portion, the disc being provided with one or more scores positioned to encourage opening of the disc on reversal thereof.
A currently preferred position for the score is around the dome portion adjacent the transition region between the dome portion and the flange portion, such a score being in a position of relatively high stress, and providing maximum free flow area for fluid subsequent to tearing of the collapsed reversed dome portion along the score.
Manufacture of such reverse buckling discs, however, poses a number of problems, both economical and practical.
One current method of manufacture is, with reference to FIG. 1, to provide a pre-form 2 incorporating a hemisphere the shape of which conforms with that of the dome portion 4 of the desired disc, to form the dome portion 4 of the disc in the pre-form 2, and then to score the dome portion 4 with an associated blade 6 whilst the dome portion is supported in the pre-form 2.
However it is necessary to provide separate tooling for each and every deliverable range of burst pressure of disc, which is clearly financially impractical.
Alternative known methods are shown in FIGS. 2 to 4, FIG. 2 showing a pre-form 8 which can be used for a range of anticipated dome heights all of which are less than that of the hemisphere 10 provided in the pre-form 8. Thus the dome portion 12 of the formed disc terminates below the hemisphere 10, and the scoring is effected by a score blade 14. However, scoring of the dome portion 12 in this manner can, as shown in FIG. 4, damage the dome portion by distorting the unscored reverse of the dome portion 12, which leads to an unreliable product and underlying issues in respect of:                repeatable performance        low product yield        range limitation        reduced in-service cycle life        high maintenance costs for tooling        inability to produce a specific burst pressure        high production costs.        
FIG. 3 shows an annular pre-form or anvil 16 with a chamfered or angled lower inner region 18 for accommodating a range of discs in a similar manner to the pre-form of FIG. 2, such an arrangement suffering from the same disadvantages detailed above in respect of FIG. 3.